Biological Principles
To understand the biological principles involved in the growth and function of the jaws, we must start with basic growth increments. We must first measure the number of mm that the condyles grow, both vertically and horizontally; and we must measure the number of mm of effective condylar growth from the gonion angle to sella horizontal.
Then we must measure the number of mm that the upper first molars grow vertically, measured perpendicular to sella horizontal at the site of the distal of the first molars, from sella horizontal to the occlusal plane. Next we measure the vertical growth of the lower first molars perpendicular to the occlusal plane, from the occlusal plane to the mandibular plane. Then we compare effective vertical condylar growth to total vertical molar growth. These procedures are the first steps in any study of the growth of the jaws or the results of treatment.
The jaws function by biological principles, which are just as dependable as physical principles such as the sun coming up in the morning and the law of gravity. The biological principle of cause and effect is just as dependable as any physical principle. Principles have been with us since the beginning of the human race and will remain through eternity.
Our literature contains no reference to "cause and effect." We have comprehensively discussed several basic principles, basic concepts and phenomena; but there has been no response from the academic world except that of Isaacson and Pancherz and their fellow workers. The relationship of vertical effective condylar growth and vertical molar growth is a principle of "cause and effect" as dependable as the law of gravity.
The effect of vertical effective condylar growth on the horizontal position of the chin is a biological principle; and the effect of posterior horizontal condylar growth on the anteroposterior position of the chin is a principle, in other words, the translation of the mandible is a principle. Also the effect of molar height on the vertical position of the chin is a principle. The condylion/gnathion distance is affected by biological phenomena. Please see Article 55 of the Schudy Chronicles.
When we have measured large numbers of cephalometric head films and observe the same relationships occurring over and over and over and over again, we begin to acquire an uncommon conviction that a given set of circumstances in the posterior portion of the jaws lead to (cause) a specific result in the anterior part of the face.
Then when we can take a given combination of changes in the posterior part of the jaws and accurately predict what effect these changes will have on the sagittal and vertical positions of the chin, when this has been repeated hundreds of times, then we begin to have an unshakable conviction that we are dealing with a principle as dependable as the law of gravity.
Equal ratios of vertical effective condylar growth and vertical first molar growth (4 mm of vertical condylar growth to 4 mm of vertical first molar growth, 5 to 5 and 6 to 6) will always cause the inclination of the mandibular plane to remain constant as it moves downward. The chin will always move forward the exact amount of the posterior horizontal condylar growth. This is a principle of jaw growth, known as "cause and effect," which is as dependable as the law of gravity. Further, the chin will move downward the exact amount of the vertical molar growth and the exact amount of the vertical effective condylar growth.
We have objectively demonstrated this in publications over a period of forty years. We have shown these principles many times in publications. The evidence is there in black and white, yet there seems to be a lack of understanding by a large segment of the orthodontic community.
As stated before, if anyone can show by objective evidence that any of these concepts and principles are incorrect, we will be forever grateful and will gladly place the information on the Schudy Chronicles.
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